City machine politics had been an important part of American urban life since the Civil War, mainly in two aspects: the political machine and the boss, its leader. Most urban historians examined the relations between the lower calss and the political machine from the Progressive's point of view or from that of the upper class. This study argues that the lower calss chose the political machine and the boss, not the Progressives, as its representatives in the legal process of election. The machine and the boss did not "steal" the vote, nor did the lower class neglect its voting right. The interaction went under way mainly based on mutual trust and recognition, not purely on material basis. The lower class elected its political representatives in this middle-class Progressive Movement through supporting the machine, and the machine in turn got the political power.